Download Reading Notes 11

Biology 30 Reading Notes
Section 11.1
Pages 374 - 382
Name:______________________
Structures and Processes of the Nervous System

______________________ is the maintenance of a constant internal
environment. Slight fluctuations ______________ and _____________ these
“normal” levels are common, so our internal systems are often said to be in a state
of dynamic _________________.

___________________ are the basic structural and functional units of the
nervous system. They are specialized to respond to _______________ and
__________________ stimuli, to conduct electrochemical signals, and to release
____________________ that regulate various body processes.

_____________ cells support neurons. These cells _______________ the
neurons, remove their ________________, and defend against
__________________. Glial cells also provide a supporting framework for all of the
nervous-system tissue.
Cells of the Nervous System
The three types of neuron are the sensory neuron, interneuron, and motor neuron.
■ _____________________ neurons gather information from sensory receptors and
transmit these impulses to the __________________ nervous system.
■ ____________________ are found entirely within the central nervous system. They
act as a ___________ between the sensory and ______________________ neurons.
They __________________ and _____________________ incoming sensory
information, and relay outgoing _____________________ information.
■ Motor neurons transmit information from the central nervous system to
_______________, glands, or other _______________ (effectors).

The basic neural pathway used is a _______________, which is a withdrawal
reflex. For example: ____________ organ (eye) detects the ball → sensory
____________ →spinal cord (_______________) → motor neuron → causes
muscle to act to withdraw (move the head) out of the way of the ball

The axons of some neurons are enclosed in a fatty, insulating layer called the
______________________, which gives the axons a glistening white appearance.
These axons are said to be _________________. The myelin sheath protects
myelinated neurons and _________________ the rate of nerve impulse
transmission.

___________________ cells, a type of glial cell, produce myelin in certain parts
of the CNS and PNS.
The Structure of a Neuron

____________________ have specialized cell structures that enable them to
transmit nerve impulses. Different types of neurons are different _______________
and _____________________.

There are four common features of a neuron, including: ________________, a
cell body (soma), an __________________ and branching ends.

___________________ are short, branching terminals that receive nerve
impulse from other neurons or ____________________ receptors, and relay the
impulse to the ___________________.

The dendrites are numerous and highly ____________________, thus
increasing the ___________________ available to receive information.

The _______________ contains the nucleus and is the site of the cell’s
____________________. It will also process the input from the
___________________.

A neuron typically has one _____________. Which can range from 1mm to 1 m,
depending on the neurons' location in the body.

The _________________ end of the axon branches into many fibres. To
communicate with adjacent neurons, glands, or muscles, the axon terminal releases
_________________signals into the space between it and the receptors or
dendrites of neighbouring cells.

The axons of some neurons are enclosed in a fatty, insulating layer called the
_____________________, which gives the axons a glistening white appearance.
These axons are said to be ____________________. The myelin sheath protects
myelinated neurons and ___________________ the rate of nerve impulse
transmission.

___________________, a type of glial cell, produce myelin in certain parts of the
CNS and PNS.
Action Potential
$
A nerve impulse consists of a series of _______________ _______________ .
$
In _______________ neurons, action potentials occur only at ___________ ____
_______________ because the myelin sheath _______________ the axonal
membrane that it encircles.
$
A neuronal membrane is said to be _______________ if the _______________
potential is reduced to less than the resting potential of ___________.
$
If the membrane at a node of Ranvier becomes _______________ to _______, a
dramatic change occurs in the membrane called an ________ _______________.
$
It is called an “ _______________ ” event because a depolarization between
-70mV and -55 mV has _______ __________.
$
Any depolarization between -55 mV up to 0 will produce _______________ action
potentials.
$
The potential difference of -55 mV is called the _____________ _____________ .
$
When the _______________ _______________ reaches threshold, special
structures in the membrane called ________-_______ sodium channels open and
make them very _______________ to sodium ions.
$
The ions are driven by their _______________ _______________ , and the
potential difference across the membrane in that tiny region of the axon is ______.
$
As a result of the change in membrane potential, the sodium channels close and
voltage-gated _______________ channels open. The potassium ions now move
down their _______________ _______________ .
$
As a result the membrane is _______________ , and the membrane potential
_______________ to nearly __________.
$
For the next few milliseconds after an action potential, the membrane cannot be
_______________ to undergo another action potential. This is called the
_______________ _______________ .
Nerve Impulse
$
A nerve impulse consists of a series of _______________ _______________ .
$
When an action potential occurs at a node of Ranvier, sodium ions flow into the
_______________ , creating a relatively high _______________ of sodium
inside the _______________ at that _______________ .
$
The sodium ions inside the axon cannot _______________ out. Instead, they
diffuse in _________ directions along the _________.
$
When the sodium ions reach _______________ nodes of Ranvier, the positive
charges _______________ the _____ __________ charge inside the axonal
membrane, causing the membrane at the nodes of Ranvier to become
_______________ to threshold.
$
At one node the membrane is _______________ , which means that it cannot be
_______________ to undergo another action potential yet.
$
The other membrane of the node is ______ _________ so the depolarization
initiates an action potential at this node.
$
The ___________process occurs at each node until it reaches the end of the
_______________ .
$
Because action potentials are forced to “__________” from one node of Ranvier to
the next due to the _______ ________ , the conduction of an impulse along a
myelinated neuron is called a _______________ _______________ .
$
The transmission of an impulse along an unmyelinated axon is much
_______________ than the saltatory conduction along a myelinated axon.
$
_______________ _______________ is caused by the breakdown of the myelin
sheath surrounding the axons in the _______________ .
$
MS is thought to be an _______________ disease, in which the body’s own
immune system breaks down the _______________ .
Signal Transmission across a Synapse
$
The simplest neural pathways have at least _________ neurons and one
connection between the neurons. (Others can involve thousands of
_______________ and their _______________ .)
$
The connection between two neurons, or a neuron and an effector, is called a
_______________ .
$
A _______________ _______________ is a synapse between a motor neuron
and a muscle cell.
$
An impulse travels the length of the axon until it reaches the far end, called the
_______________ _______________ .
$
Most neurons are not directly _______________ , but have a gap between them
called the _______________ ___________.
$
Chemical messengers called ___________________________ carry the neural
signal from one neuron to another or signal from one neuron to another, or from a
neuron to an _______________ .
$
When an action potential arrives at the end of a presynaptic neuron, the impulse
causes sacs that contain _______________ to fuse with the membrane of the
_______________ . These sacs, called _______________ ___________,
release their contents into the synaptic cleft by _______________ . The
neurotransmitters then diffuse across the synapse to reach the _______________
of the postsynaptic _______________ , or cell membrane of the
_______________ .
$
Upon reaching the postsynaptic membrane, the neurotransmitters bind to specific
receptor _______________ in this membrane.
$
Neurotransmitters have either _______________ or _______________ effects
on the postsynaptic membrane.
$
If the effect is _______________ , the receptor proteins will trigger ion channels
that open to allow positive ions, such as _______________ , to flow into the
postsynaptic neuron. As a result, the membrane becomes slightly
_______________ .
$
If the neurotransmitter is _______________, the receptor will trigger
_______________ channels to open, allowing potassium ions to flow out. This
results in a more negative transmembrane potential, resulting in
_______________ .
$
A single cell body may be receiving signals from many _______________
neurons at the same time.
$
One of the functions of the cell body is to _______________ all of the incoming
signals.
$
If the _______________ stimuli are strong enough, the _______________ will
reach the point at which the _______________ is connected to the cell body and
an impulse will be generated.
$
The _______________ neuron will then return to ____________ ___________ .
$
After the _______________ has had its effect, _______________ break it down
and _______________ it so that its components can be reabsorbed by the
_______________ _________.
Neurotransmitters in Action
$
_______________ is a _______________ that crosses a neuromuscular
junction. It _______________ the muscle cell membrane, causing
_______________ and _______________ of muscle fibre.
$
Cholinesterase is released into a synapse, where it breaks down
_______________ . It is one of the _______________ acting enzymes. It allows
the ion channels to close and the membrane to _______________ in a fraction of
a second. ( A nerve gas called __________ destroys this function by blocking the
release of cholinesterase into the _______________ junction.)
$
Several neurological disorders have been linked to _______________
_______________ or _______________ production.
$
Certain drugs can alter the proper action of _______________ .